The present invention relates to an arrangement for generating a hydrogen-containing gas.
Arrangements of this type are known, for example, as mobile methanol reforming systems for fuel-cell-operated motor vehicles in order to provide the hydrogen required for the fuel cells. Particularly for this mobile application, there are the requirements (1) of rapidly reacting to typical load changes in the vehicle, and (2) of being able to supply hydrogen for the fuel cells as fast as possible after the system start, and achieving this by means of a relatively compactly constructed reforming system.
As known, the water vapor reforming reaction for reforming a hydrocarbon, such as methanol, takes place endothermally and at a reaction temperature increased with respect to room temperature. In the case of a cold start of the reforming system, hydrogen can therefore not be provided immediately with water vapor reforming. On the contrary, the components of the system must first be brought to a corresponding operating temperature. Specifically, in fuel-cell-operated motor vehicles, there is a desire to reach the warmed-up normal operation as fast as possible in order to feed the fuel cells as early as possible with hydrogen generated in a continuous driving operation.
Various measures have been suggested for an accelerated cold start of a reforming system. Thus, it is suggested in U.S. Pat. No. 5,516,344 to integrate the reformer together with a carbon monoxide shift converter connected behind it in a common housing to which a burner is assigned that burns a supplied combustible mixture. As a result of the hot combustion exhaust gases, among others, the reformer and the carbon monoxide shift converter are heated.
In German Patent Application DE 197 54 012, a reformer and a carbon monoxide removal unit are each constructed in several stages and the stages of the reformer and the carbon monoxide removal units each form a heat transfer structure. In this case, the carbon monoxide removal unit is composed in a modular manner of a carbon monoxide oxidation unit and of a carbon monoxide shift reaction unit.
Despite the improvement in the dynamics of such systems, a further increase of the dynamics is desirable for fast load changes and for a large load spread in mobile applications. It is an object of the present invention to provide an arrangement for generating a hydrogen-containing gas from a hydrocarbon-containing medium in which the above-mentioned problems are improved.
According to the present invention, the stages of a reforming unit in an ascending order relative to a gas flow direction in the reforming unit are thermally coupled with stages of a carbon monoxide removal unit in a descending order relative to the gas flow direction of a reformate in the carbon monoxide removal unit, which reformate is provided by the reforming unit and is supplied to the carbon monoxide removal unit. The coupling of the stages takes place by way of a heat-conducting separating medium so that the stages of the reforming unit and of the carbon monoxide removal unit are each in a thermal contact with one another. The special advantage of the present invention is that the temperatures in the reforming unit, in the case of a full load, permit good utilization of the used reforming catalyst. The last coupled carbon monoxide removal stage only has a low carbon monoxide concentration, in which case, in a particularly advantageous manner, also a carbon monoxide formation can be prevented by a so-called reverse shift reaction at a small load. Likewise, by means of the improved dynamics, fast load changes are possible while the load spread is large.
In a preferred embodiment of the present invention, the gas flow direction in the reforming unit and in the carbon monoxide removal unit take place in the same direction.
A particularly preferred embodiment is a two-stage arrangement of the reforming unit and the carbon monoxide removal unit. It is advantageous to provide a carbon monoxide oxidation stage as the carbon monoxide removal unit. In this case, it is particularly advantageous to connect the first stage of the reforming unit with the second stage of the carbon monoxide removal unit and to connect the first stage of the carbon monoxide removal unit with the second stage of the reforming unit.
An arrangement of the reforming unit and the carbon monoxide removal unit in a joint housing is particularly compact. In this case an advantageous thermal coupling between the modules is possible.